The tokens of the form :something are host variables, that is, they refer to variables
in the C program. They are explained in Section 32.6.

In the default mode, statements are committed only when
EXEC SQL COMMIT is issued. The embedded
SQL interface also supports autocommit of transactions (similar
to libpq behavior) via the
-t command-line option to ecpg (see below) or via the EXEC SQL SET AUTOCOMMIT TO ON statement. In
autocommit mode, each command is automatically committed unless
it is inside an explicit transaction block. This mode can be
explicitly turned off using EXEC SQL SET
AUTOCOMMIT TO OFF.